I don't know anything about stamp collecting.
If I were you and I was looking to sell, I'd start with a plan like this...
A) Research the possible values. Go to the library and find some stamp collecting books. Search the internet for stamp collecting sites. Search ebay for similar listings and sales. This would be time consuming, but could be worth it in the end. It could also be a fun family activity.
B) Find a local stamp collector and ask him/her to take a look at the collection and appraise. I would not suggest leaving the book with anyone.

If they make you an offer, it would most likely be much, much lower than the real value.
C) Take a buncha, and I mean
buncha pictures or scans (maybe all pages?) and list them on ebay; per stamp, per page, entire collection, your call. This could let the market decide the value. Of course, you'd want to time your auction well and hope that the most collectors as possible see it.
D) All of the above. Determine a value though research and appraisals. List them in an auction(s) with a starting price or reserve price somewhere between the offer and the appraisal.
Good luck!